United States Nuclear Regulatory Commission - Protecting People and the Environment

Engineered Covers for Waste Containment: Changes in Engineering Properties and Implications for Long-Term Performance Assessment (NUREG/CR-7028, Volume 1)

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Publication Information

Manuscript Completed: July 2010
Date Published:
December 2011

Prepared by:
C.H.Benson1, W.H. Albright2, D.O. Fratta1, J.M. Tinjum1,
E. Kucukkirca1, S.H. Lee1, J. Scalia1, P.D. Schlicht1, and X. Wang1

1Geological Engineering
University of Wisconsin-Madison
1415 Engineering Drive
Madison, WI 53706

2Desert Research Institute
2215 Raggio Parkway
Reno, NV 89512

Jacob Philip, NRC Project Manager

NRC Job Code N6366

Prepared for:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

This peer-reviewed study demonstrates that engineering properties of cover soils change while in service and that long-term engineering properties should be used as input to models employed for performance assessments. Recommendations for appropriate input are made based on the data that were collected. Increases in the saturated hydraulic conductivity, saturated volumetric water content, and the air entry suction (as characterized by van Genuchten’s α parameter) occurred due to formation of soil structure, regardless of climate, cover design, or service life. Substantial changes in hydraulic conductivity were observed in some geosynthetic clay liners (GCLs) that did not hydrate completely and underwent cation exchange. Changes in geomembranes and geosynthetic drainage layers were modest or small, and computations based on antioxidant depletion rates suggest that the minimum service life of geomembranes is on the order of 50-125 yrs (the actual service life will be longer). The findings indicate that covers should be monitored to ensure that they are functioning as intended. Monitoring using pan lysimeters combined with secondary measurements collected for interpretive purposes is recommended. Future research investments should include an evaluation of remote sensing technologies for cover monitoring and analog studies to estimate properties of earthen and geosynthetic cover materials corresponding to service lives of 100s to 1000s of years.